Indicating means for thermal circuit interrupters



March 11, 1947. A. H. POWELL 2,417,263

INDICATING MEANS FOR THERMAL CIRCUIT INTERRUPTERS Filed June 3, 1944 v Inventor;

Ahfic H- Powell,

His Attorney- Patented Mar. 11, 1947 INDICATING MEANS FOR THERMAL CIRCUIT INTERRUPTERS Alric H. Powell, Yeadon, Pa., assignor to General Electric Company, a corporation of New York Application June 3, 1944, Serial No. 538,575

4 Claims.

My invention relates to improvements in electric circuit interrupting devices such as fuses for protecting high voltage electric circuits. Specifically my invention is an improvement on my prior Patent 2,343,224, granted February 29, 1944, and assigned to the same assignee as the present application.

High voltage fuses which consist in the main of a fusible element in the form of one or more conductors of suitable metal such as silver or zinc embedded in a granular, inert, or refractory arc extinguishing material of high dielectric strength such as sand, or relatively finely divided quartz, are known. Such power fuses, usually called fuses of the enclosed type or current limiting fuses, are capable of interrupting currents of large magnitude without noise, discharge of liquid or solid particles or production of gases which must either be discharged to atmospher or dissipated in a high pressure chamber.

It is an object of my invention to provide a new and improved circuit interrupting device of the above mentioned type which is simple and inexpensive to manufacture, sturdy in construction and very emcient in operation.

It is another object of my invention to provide a high voltage fuse of the sand filled type which may be manufactured and assembled at a much lower cost than similar devices used heretofore, and yet which gives superior operation from an interrupting standpoint.

Further objects and advantages of my invention will become apparent as the following description proceeds and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

For a better understanding of my invention ref erence may be had to the accompanyin drawing in which Fig. l is a sectional view of an exemplary form of high voltage fuse constructed in accordance with my invention and showing the indicating means for the fuse in the nonindicating position; Fig. 2 is a view, partly in section, of a portion of the fuse in Fig. 1 showing the indicator in the position it would assume upon rupture of the fusible element; Fig. 3 is a sectional view taken on line 3--3 of Fig. 1; Fig. 4 is a perspective view of the indicator housing associated with the fuse rotated 90 with reference to Fig. 1, and Fig. 5 is a top view of the indicator housing of Fig. 1.

Although it will be evident that certain parts of the present invention may be practiced to advantage with different types and forms of electric fuses, the invention lends itself most advantageously to practice with the enclosed type of fuse such as is disclosed, for example, in United States Letters Patent 2,29%,132, granted August 25, 1942, upon an application of C. L. Schuck and assigned to the same assignee as the present application, wherein the fusible conductor is shown as being enclosed in a tubular casing of suitable insulating material and surrounded by or embedded in a pulverulent or sandy arc quenching material.

Referring now to the drawing, I have illustrated an electric fuse device which has a housing structure or casing I, of open ended tubular form constructed of suitable insulating material such as glass, porcelain, fiber, or the like. Within tubular housing I there is provided an elongated insulating support or core 2, comprised of high heat-resisting ceramic or other suitable material. This core extends longitudinally of casing I and serves to support a current interrupting element 3 which is spirally wound on the core, as is clearly indicated in Fig. 1. Although the current interrupting element 3 of the illustrated device comprises only a single conductor, it is common in the construction of such fuses which are generally referred to as of the current limiting type, to employ one or more main conductors depending upon the current rating. This is for the reason that it has been found that most effective limiting action is produced when conductors of very thin cross section are employed. Hence, where the current rating demands a relatively large total cross section it is desirable to divide this total cross section into a number of parallel connected conductors having thin cross section, such as a plurality of fine wires. The interior of casing I around core 2 is filled with an inert, granular arc quenching material i, such as sand or pulverized quartz which embeds the current interrupting element 3. As will be seen from the sectional view of Fig. 3, the core 2 is of generally star-shaped form in that it has a plurality of longitudinally extending fins or ribs 5. Although the illustrated core 2 has four such fins 5, a core having more or less than four fins may be employed depending upon the rating and size of the particular fuse. The advantage of a star-shaped core is that the current interrupting element 3 touches the core 2 only at spaced points so that the maximum length of the element is exposed to the filler material i. Spirally winding the interrupting element 3 on core 2 permits the installation of an element of relatively great length in a casing of practical dimensions.

In order to close the ends of tubular housing or casing I, I provide suitable end caps or closure members 6 and i, which are generally saucershaped. End cap 6 illustrated as the upper end cap, is substantially identical with the lower end cap '2 except that the latter is provided witha recessed opening which will be described'lierein-- after.

As shown in the drawing,.theseend caps 6 and I are each provided with an interlocking" means illustrated as an oif-set: shoulder 8 and they are adapted to be held in sealed relationship with tubular housing or casing I by metallic ferrules 9, which are molded or die cast around theqends oftubular casing! so as to envelope the off-set shoulders 8 of endcaps 6. and I,

while. permitting the major portion; of theend caps to. remain exposed. As will bedescribed hereinafter the metallic ferrules 9 are electriecally connected: with the circuit interrupting element. 3 and consequently provide the upper and,.lo.w,er. terminals of the fuse device. Al-

thoughvl. have. specifically shown the interlocking means, as comprising anoff set shoulder. 8, it should. be. understood that such interlocking means-might equally well consist of, pin pricks, corrugations, knurlings, or grooves of some sort.

Furthermore, the inherent irregularities of the.

to set forththe. fuse size or any other. pertinent information.-

Lower,e11d,cap I, as was mentioned above, is

provided with a recessed hole or opening It), intotwhich isfastened a'spring. support II as by,

peeping. over. the; ends. thereof, as is clearly shownin Figs. 1 and 2. This spring. support I! has an outside thread to which may be threadedly; mounted a tubular target or indicator housing. I2 constructed of fiber, glass or other suitable insulating material. Reciprocatingly mounted withintubular housing i2 and adapted to extend out ofopening II! in lower end cap I, isanindicatoror plunger I3 which is provided witnan enlarged portion M. A. suitable compression spring I5 mounted in spring support II. andbearing against enlarged portion Id of indicator ie constantly biases plunger or indicator 13- to the. indicating position shown in Fig. 2.

Incrder to maintain plunger or. indicator I3 in thenonindicating position shown in Fig. 1, the upper end of tubular. indicator housing I2 is substantially. closed except for a small central opening it extending along the axis oftub ular" indicator housing I21 A suitable tension spring H has one end thereof fastened to the plunger or indicator I3 as indicated at I8, while the other end thereof is fastened to a strain or supporting wire I9 which in turn extends through the small opening IS. The portion of strain Wire I9 extending outside of indicator housing I2 is passed through small openings 20 in the upper end of indicator housing I 2, which openings are arranged substantially perpendicular to the opening it, and is twisted about itself so as to place sufficient tension on tension spring I'I to maintain the. indicator I3 in the nonindicating position shown in Fig. 1. When tension spring I! is stressed as shown in Fig. 1, the plunger I3 is held in a floating condition with a substantially constantforce. applied to strain wire I9, whereupon jarring or rough handling of the fuse device will not harm or cause rupture of strain wire Ilia It willbe obvious that compression spring I5 mustbe'a weaker spring than tension spring If... Withthe floating construction of plunger l3 described above, a much weaker strain wire I 9 maybe used without danger of stretching or rupturing to permit the indicator or plunger I3 to move to the indicatingposition. shown in Fig. 2. I havediscovered that without the use. of tension springl'l, strain-wire I9 must be able to withstandten or more times the force of. spring means- I? to prevent movement of I the.

plungerv it out. of its nonindicating position merely due to normal handling of the fuse device. The floating arrangement of the indicator is disclosed and claimed in; my prior Patent 2,3432%, referred to above.

It is desirable-to obtain. operation of. the indicator. comprising plunger. I3- in response to rupture of thefuse linkv orcircuit interruptingelement 3 and to this end I provide an indicator wire fzi which'is also wound on star-shaped core 2 in aspiral manner'andpreferably between turns of thecircuit interrupting or fusible element As will. be describedhereinafter, the

upper end of the indicator wire 2i is electrically connected tow-upper terminal ferrul 9. 1' The lower end of; indicator wire;2I ispassedthroughsmall openings-22in indicatorhousing i22 Thesesmall openings,.22 are arranged parallel to openings.

26 and I displaced from the axis of indicator housing I2 by a certaindistanceso; thatwhen indicatorwire extendsthrough openings; 22- a gap 23. is provided asis clearly shown in Fig. 4,

between strain wire lil and, indicator wire 2I-. I have found that a gapof s; of an inch is satisfactoryfor thepurpose to be describedlhere- Wire t9, which potentialproduces arcing across,

the gap with.consequentruptureof strain wire [9 either by melting due; to current flowing therethrough or; by the direct, heatof; the. .arc which; will causev rupture: even. at. very." low: cur.- rents.

In order to causeproper operation of the. fuse device described, above on long continued. overload conditions, it isdesirable to provide-one or morethermal chambers. such asare generally indicated at. 24 m Fig. 1. Preferably; these thermal chambers may be constructed in accordance with those disclosed and claimed in my prior patent referred to above.

In constructing or assembling the fuse device of Fig. 1 the indicator housing i2 is first fastened to lower end cap l, as is clearly described above with the plunger element suitably maintained in the non-indicating position. The star-shaped core 2 is then mounted nextto the indicator housing I2 and is bound to the tube by a binder comprising a plurality of turns of wire, cord, or the like, indicated at in Fig. 1. Before the core 2 is fastened to indicator tube I! it has applied thereto at either end thereof terminal elements 26 substantially identical with the terminal elements disclosed and claimed in the above mentioned Schuck patent. These terminal elements comprise a looped portion 21 for fitting around one of the ribs 5 of core 2. The lower terminal 26 is first suitably welded to the lower end of fusible or interrupting element 3 and is securely bound to core 2 by the binder 25 which also holds core 2 to housing l2. Then the fusible element 3 is wound on the core with the upper end thereof having been welded to upper terminal 26. This upper terminal 23 is securely bound to core 2 by a plurality of turns of wire indicated at 28. Each of the terminals 26 is provided with an extension 29 which is adapted to extend outside of casing I so as to be enveloped by the molded or die cast ferrules 5 and, consequently, electrically connected thereto. The target element or indicator wire 2| is then passed through the openings 22 of indicating housing I 2 and is twisted back upon itself to securely fasten it within openings 22. This indicating wire is then wound spirally on core 2 g with its turns between the turns of the main circuit interrupting element 3, and the upper end of the indicator wire is fastened to the plurality of turns of wire forming the binder 28 for holding upper terminal 26 to core 2. At this stage preferably the holes I5, 20 and 22 in the indicator housing l2 are filled with a suitable cement to prevent the arc quenching material from escaping through these openings.

It will be observed then, that the lower end cap I, the/indicator housing l2 and associated indicator parts, the core 2 with the fusible element and indicator wire wound thereon, and the upper and lower terminals 26 fastened thereto, comprise a sub-assembly of the fuse device which may be placed in the tube or housing I so that the latter may be filled with granular material while the upper end cap 5 is removed therefrom. As soon as the housing I is filled with the granular arc quenching material the upper end cap 6 is placed into position and the fuse device is placed in a die casting machine whereupon the ferrules 9 are cast into place completely sealing the unit and providing the ferrules for the fuse device.

With my improved construction described above it is possible to preassemble a number of the elements into a sub-assembly which is easily handled without getting the elements out of place or damaging the main fusible element or the indicator wire. Thus the fuse device of my invention, while being simple in construction, greatly simplifies the manufacturing processes with consequent cost reduction.

Although I have elected to describe and illustrate herein a preferred embodiment of my invention as employed in a fuse device as well as the process of construction thereof, it is contemplated that other applications of my invention to fuses or like electrical devices other than the particular form illustrated, will suggest themselves to those skilled in the art. It is intended that such other applications or modifications as do not depart from the true spirit and scope of my invention will be covered by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a, circuit interrupting device having an interrupting element including a conductor spirally wound on an insulating support having 1ongitudinally extending ribs for maintaining the conductor in spaced relation to a central body portion of the support, an indicating means for said device including a housing therefor, means for fastening said indicator housing to said insulating support, an auxiliary fusible element within said housing and attached thereto, and a cooperating auxiliary conducting element spirally wound on the insulating support intermediately of the turns of said conductor and having a portion passing through said housing to define therein a gap between such portion and said auxiliary fusible element.

2. In an electric circuit interrupting device in- 1 eluding an insulating casing, an end cap for closing one end of said casing, an indicator housing extending longitudially within said casing and supported from said end cap, a longitudinally ribbed insulating support in said casing having one end thereof engaging said end cap, means for holding said housing end cap and support as a unitary assembly, a pair of terminals one supported from each end of said support and each having a portion thereof extending outside of said casing, .a circuit interrupting element including a conductor spirally wound on said support and interconnecting said terminals, an auxiliary fusible element within said housing and attached thereto, a cooperating auxiliary conducting element spirally wound on said support intermediately of the turns of said conductor and having a terminal portion passing through said housing to define therein a gap between such portion and said auxiliary fusible element an inert granular arc extinguishing material within said casing embedding said conductor and the part of said auxiliary conducting element outside of said housing, an end cap for closing the other end of said casing, and a ferrule of conducting material at each end of said casing for sealing the casing and enveloping the portions of said terminals extending outside of the casing so as to be electrically connected to said conductor.

3. In an electric circuit interrupting device the combination with an insulating enclosing casing, a fusible element therein, an indicator for indicating operation of said circuit interrupting device comprising a housing of insulating material supported from one end of said enclosing casing, an auxiliary fusible element within said housing and attached thereto, and a cooperating auxiliary conducting element arranged outside of said housing and having a terminal portion passing through the housing to define therein a gap between such portion and said auxiliary fusible element.

4. In an electric circuit interrupting device, the combination with an enclosing casing, a fusible element therein, means for supporting said fusible element in said casing, an indicator for indicating operation of said circuit interrupting device comprising a housing supported within said casing from one end thereof, an auxiliary fusible element within said housing and attached thereto, an 9 auxiliary conducting. element arranged within said. casing; outside of izsaidr housing wand hav-ingna; terminal portion passing: through theing f0r-mechanica11y securingeaid supporting means to saidend capt- ALRIC' I-I.--POWELL;

REFERENGES. CITED,

The-following references ,areof record in the.

:fil'e of this patent:

UNITED STATES PATENTS Number;

Na'me Date Powell Feb. 29, 1944 Dannenberg Oct; 1,. 1940 Schuck Aug. 25, 1942 Serfling et a1 Dec. 28; 1943 Biermanns et a] Dec. 22, 1942' WilliamsJr Sept. 1, 1942 Klein June 10, 1941 Andersen et 2x1- Nov; 2, 1943 Hubbard Feb. 2, 1943' Thommen' et 21;. Jan; 28', 1941 Rankin-4 Jan. 30, 1940' VanNuis- Ju1y4, 1893 

